The invention relates to a belt drive for a machine for processing flat printing materials, having an endless belt revolving during operation, a roller about which the belt is partially looped, a frame with respect to which the roller is adjustable between a working position, wherein the roller keeps the belt in tension, and a position moved away from the working position, wherein the belt is not in tension, and a spring device for biasing the roller into the working position thereof, as well as for a machine for processing flat printing materials, in particular, a rotary printing machine, having a conveying station in the form of a feeder, for supplying sheets to a first processing station, and a conveying station in the form of a delivery, for feeding sheets accepted from a last processing station to a pile-forming or stacking station, the conveying stations being equipped with belt drives.
A belt drive of the foregoing general type has become known heretofore from, for example, the published German Patent Document DE 197 12 690 A1. A spring device which is disclosed in this document for biasing the roller into the working position thereof is constructed, in one exemplary embodiment, as a compression-spring device, wherein a compression spring acts between an abutment linked to a frame, and a lever connected to a tensioning shaft in the form of an eccentric shaft rotatably mounted in the frame, the lever being fixed against rotation relative to the rotatable eccentric shaft. Under the action of the compression spring, an eccentric section of the tensioning shaft is set against a carriage rotatably bearing the roller and being displaceable with respect to the frame. An end of the lever facing away from the tensioning shaft is connected by a hinge to a nonrotatable threaded pin which, through the intermediary of an adjusting nut cooperating therewith and supporting it on the abutment, is withdrawable into an opening formed in the abutment, thereby, in effect, shortening the compression spring. By a rotation of the tensioning shaft, which accompanies the shortening of the compression spring, the shaft assumes a rotational position wherein the roller is adjustably displaced from the working position thereof into the position moved away therefrom. In this moved-away position, the endless belt can be drawn onto the roller and drawn off the latter, respectively. To change the belt if it should become worn, a screwing operation is needed in order to remove the tension of the belt which is to be drawn off, and a further screwing operation is necessary in order to apply tension to a newly drawn-on belt.
It is accordingly an object of the invention to provide a belt drive of the type mentioned in the introduction hereto, for changing which, measures have been simplified, and require the least possible expenditure of time.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a belt drive for a machine for processing flat printing materials, comprising an endless belt revolving during operation, a roller about which the belt is partially looped, a frame with respect to which the roller is adjustable between a working position, wherein the roller keeps the belt tensioned, and a position moved away from the working position, wherein the belt is untensioned, a spring device for biasing the roller into the working position thereof, a double crank by which the roller is articulated with the frame, and a stop which, due to a change in position of the double crank from a position corresponding to the working position of the roller into a position corresponding to the moved-away position of the roller, is carried out to a given extent beyond a dead-center position of said double crank, preventing a change in position beyond said given extent.
In accordance with another feature of the invention, the double crank is formed by an eccentric shaft and a guide rod articulated eccentrically therewith.
In accordance with a further feature of the invention, the stop is formed on the eccentric shaft and, in the position of the double crank corresponding to the moved-away position of the roller, butts against the guide rod.
In accordance with another aspect of the invention, there is provided a machine for processing flat printing materials, comprising a conveying station in the form of a feeder for supplying sheets to a first processing station, and a conveying station in the form of a delivery for feeding sheets accepted from a last processing station to a sheet pile station, at least one of the conveying stations being equipped with a belt drive, including an endless belt revolving during operation, a roller about which the belt is partially looped, a frame with respect to which the roller is adjustable between a working position, wherein the roller keeps the belt tensioned, and a position moved away from the working position, wherein the belt is untensioned, a spring device for biasing the roller into the working position thereof, a double crank by which the roller is articulated with the frame, and a stop which, due to a change in position of the double crank from a position corresponding to the working position of the roller into a position corresponding to the moved-away position of the roller, is carried out to a given extent beyond a dead-center position of the double crank, preventing a change in position beyond the given extent.
In accordance with a concomitant feature of the invention, the machine for processing flat printing materials is a rotary printing machine.
In order to achieve the objective of the invention, there is thus provided a double crank, by the aid of which the roller is articulatedly secured to the frame, and also a stop which, upon the occurrence of a change in the position of the double crank from a position corresponding to the working position of the roller into a position corresponding to the moved-away position of the roller, which is carried out to a specific extent beyond a dead-center position of the double crank, prevents a change in position beyond the specific extent.
Through the use of the double crank, in order to displace the roller between the working position thereof and the position thereof moved away therefrom, it is merely necessary to pivot an arm of the double crank out of a position of the arm on this side of a dead-center position of the double crank into a position on the other side of this dead-center position and the reverse. By comparison with a screwing operation for tensioning or relieving the tension on the belt in the case of the aforementioned heretofore known belt drive, a pivoting action of this type is a measure which is comparatively simple and may be performed relatively quickly.
In a particularly advantageous construction, the double crank is formed by an eccentric shaft and a guide rod or lever articulatedly connected eccentrically thereto. This permits the particularly simple introduction of a pivoting movement into one arm of the double crank, namely, as a result of rotating the eccentric shaft, respectively, less than one complete revolution.
In a preferred exemplary embodiment, the stop is formed on the eccentric shaft and, in the position of the double crank corresponding to the moved-away position of the roller, is butted against the guide rod. Therefore, no features other than the double crank are needed in order to lock the latter, under the action of the spring device, in the position of the double crank corresponding to the moved-away position of the roller.
The invention is explained in greater detail with regard to the figures of the drawings, the details of which reproduce areas of use of the belt drive in connection with a machine which sets images on flat printing materials, and a preferred exemplary embodiment of the belt drive, and wherein identical parts are identified by like reference characters.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a belt drive for a machine for processing flat printing materials, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: